The present invention related to an actuator for use with small globe valves used to control fluid movement in heating and cooling systems.
Small electric and electronic control valves are in use in thousands of applications, primarily with hot or chilled water for the control of temperature but also for humidity, etc. and also for other mediums such as steam, glycol, heat-transfer oils, etc. In all cases, the main problems are cost, silence of operation (since they are located in or close to the occupied suites), and that they be compact (since they are usually located in confined cabinets, etc.). They replace the older pneumatic valves previously used in heating and cooling systems by that industry a decade or two ago.
The problems which plague the manufacturers are many, including, the cost of manufacture, the quietness of the miniature gear trains, detecting and stopping the actuator at the correct force and/or protecting the overload of the motor or valve, and stopping by a switch the actuator at the full open position, particularly with respect to the cost of the switches themselves, and the mechanical force balancing system necessary to detect the force applied by the actuator.
Other requirements often involve providing a spring to drive the motor open or closed in the event of a power failure for safety reasons as for example, described in my U.S. Pat. No. 6,100,655 issued Aug. 8, 2000.
Common current solutions to these problems involve the installation of a magnetic clutch in the gear train. Over a given torque, the gear train slips, allowing the motor to continue running without further strain. Often this helps with the problem of noise as well, since the impact of the small teeth does not travel through the gear train as much To stop the motor, a thermostatic device, usually a computer-based device, is programmed only to run for a few minutes to assure that the valve will be fully closed or fully open, etc. The run time programmed is just greater than the run time of the actuator. This eliminates the end switches and load sensing devices otherwise needed, although it incurs other complications and other problems (since some computer based systems constantly jog the actuator to check the position, closed or open etc., and constantly drive wear their primary gears, energizing the motor every 2 or 6 minutes year ""round promoting wear and tear).
Other methods of detecting high load are possible with certain motors where the amperage of the motor is proportional to load and an electronic detecting circuit is arranged to shut the motor. In these cases, constant checking of status causes the motors to burn out.
The design of the motor described herein differs in that it still achieves low cost of production, but it operates quietly without clutches, etc. It is inexpensive to build (once the tooling is amortized), and it actually shuts off and stays so without the need to constantly jog the motor since it also inherently provides a feedback circuit to transmit the open/closed positions of the control valve, an important need in today""s automated systems.
In accordance with the present invention there is provided an actuator for opening and closing a globe valve. The globe valve has a stem through which positioning of the globe valve is achieved. The globe valve is normally based to open position. The actuator comprises an electric motor which drives a worm and pinion arrangement. The pinion drives an output gear which gear is movable between a base and a raised position within a frame and held in the base position by a compression spring with a similar compression rating to that of the required valve shut off. The output gear drives a worm stem bearing against the stem of the globe valve to move it against its bias in one direction to close the globe valve. The output gear and worm stem are arranged so that, when the globe valve is fully closed, the worm stem is at its extreme position in that one direction and the output gear then begins to move within its frame from its base to its raised position. A shoulder on the output gear simultaneously moves a first leaf spring to break contact with a first switch and turn off the electric motor with the valve in closed position. In the opposite direction, the output gear returns to its base position and then moves the worm stem in an opposite direction to a position where the worm stem moves a second leaf spring to break contact with a second switch to turn off the electric motor with the valve in open position.
In a preferred embodiment, the motor and first and second switches are mounted on a printed circuit card together with a power source. The printed circuit card is arranged with appropriate circuitry for running the motor.
The actuator according to the present invention is so quiet as to be undetectable to the average human ear. It uses no slipping clutches, requires no xe2x80x9ctime outxe2x80x9d circuits or software, is not affected or worn by jogging or computer check-position pulses and is not dependent on electronic load detecting (theoretically force detecting) circuits and software.